Irrigation systems employing drip irrigation lines may include valves for allowing liquid to flow through the drip lines of the system. Such valves for example may include flushing valves that are installed at an end of a drip line for affecting flushing of the line.
U.S. Pat. No. 5,535,778, the disclosure of which is incorporated herein by reference, relates to a self-closing valve that is used for flushing irrigation lines. This valve has an inlet portion that communicates with water of an irrigation line, and an elastic membrane that divides an enclosed space in the valve into upstream and downstream compartments. The valve has a passage between the compartments and a discharge opening in the upstream compartment. Flow of water from the upstream compartment flowing into the downstream compartment flexes the membrane in the upstream direction until it closes against the discharge opening to end flushing and remain closed as long as it is exposed to upstream pressurized water from the irrigation line. Upon drop and cessation of the upstream pressure, the membrane will return to its un-flexed state and the valve will be ready for a subsequent flushing action that will begin when exposed again to an upstream pressurized water in the irrigation line.
WO2012131503 which corresponds to US 2014014202, the disclosure of which is incorporated herein by reference, is an example of an eternally controlled valve that has a liquid passage, a sealing diaphragm and a control port that can receive pressurized control signals. The sealing diaphragm is adapted to seal the passage, where upon receipt of a control signal the sealing diaphragm bends and opens a path for liquid around the sealing diaphragm that can flow downstream. Cessation of the control signal will allow the valve to return back to a close state where pressurized liquid upstream is stopped from flowing downstream.
In irrigation systems employing a plurality of valves, each controlling liquid flow into and/or out of a section of the system, variance in the liquid flow rate through the system may depend on the amount of valves that are activated to open during the same period of time. The larger the number of valves that open simultaneously the larger the variance in flow rate that the system must be designed to support.